Microfluidic devices, as understood herein, include fluidic devices over a scale ranging from microns to a few millimeters, that is, devices with fluid channels the smallest dimension of which is in the range of microns to a few millimeters, and preferably in the range of from about 10's of microns to about 2 millimeters. Partly because of their characteristically low total process fluid volumes and characteristically high surface to volume ratios, microfluidic devices, particularly microreactors, can be useful to perform difficult, dangerous, or even otherwise impossible chemical reactions and processes in a safe, efficient, and environmentally-friendly way. Such improved chemical processing is often described as “process intensification.”
Process intensification is a paradigm in chemical engineering which has the potential to transform traditional chemical processing, leading to smaller, safer, and more energy-efficient and environmentally friendly processes. The principal goal of process intensification is to produce highly efficient reaction and processing systems using configurations that simultaneously significantly reduce reactor sizes and maximize mass- and heat-transfer efficiencies. Shortening the development time from laboratory to commercial production through the use of methods that permit the researcher to obtain better conversion and/or selectivity is also one of the priorities of process intensification studies. Process intensification may be particularly advantageous for the fine chemicals and pharmaceutical industries, where production amounts are often smaller than a few metric tons per year, and where lab results in an intensified process may be relatively easily scaled-out in a parallel fashion.
Process intensification consists of the development of novel apparatuses and techniques that, relative to those commonly used today are expected to bring very important improvements in manufacturing and processing, substantially decreasing equipment-size to production-capacity ratio, energy consumption and/or waste production, and ultimately resulting in cheaper, sustainable technologies. Or, to put this in a shorter form: any chemical engineering development that leads to a substantially smaller, cleaner, and more energy efficient technology is process intensification.
The methods and/or devices disclosed herein are generally useful in performing any process that involves mixing, separation, extraction, crystallization, precipitation, or otherwise processing fluids or mixtures of fluids, including multiphase mixtures of fluids—and including fluids or mixtures of fluids including multiphase mixtures of fluids that also contain solids—within a microstructure. The processing may include a physical process, a chemical reaction defined as a process that results in the interconversion of organic, inorganic, or both organic and inorganic species, a biochemical process, or any other form of processing. The following non-limiting list of reactions may be performed with the disclosed methods and/or devices: oxidation; reduction; substitution; elimination; addition; ligand exchange; metal exchange; and ion exchange. More specifically, reactions of any of the following non-limiting list may be performed with the disclosed methods and/or devices: polymerisation; alkylation; dealkylation; nitration; peroxidation; sulfoxidation; epoxidation; ammoxidation; hydrogenation; dehydrogenation; organometallic reactions; precious metal chemistry/homogeneous catalyst reactions; carbonylation; thiocarbonylation; alkoxylation; halogenation; dehydrohalogenation; dehalogenation; hydroformylation; carboxylation; decarboxylation; amination; arylation; peptide coupling; aldol condensation; cyclocondensation; dehydrocyclization; esterification; amidation; heterocyclic synthesis; dehydration; alcoholysis; hydrolysis; ammonolysis; etherification; enzymatic synthesis; ketalization; saponification; isomerisation; quaternization; formylation; phase transfer reactions; silylations; nitrile synthesis; phosphorylation; ozonolysis; azide chemistry; metathesis; hydrosilylation; coupling reactions; and enzymatic reactions.
The present inventors and/or their colleagues have previously developed various microfluidic devices useful in process intensification and methods for producing such devices. These previously developed devices include apparatuses of the general form shown in prior art FIG. 1. FIG. 1, not to scale, is a schematic perspective showing a general layered structure of certain type of microfluidic device. A microfluidic device 10 of the type shown generally comprises at least two volumes 12 and 14 within which is positioned or structured one or more thermal control passages not shown in detail in the figure. The volume 12 is limited in the vertical direction by horizontal walls 16 and 18, while the volume 14 is limited in the vertical direction by horizontal walls 20 and 22.
The terms “horizontal” and “vertical,” as used in this document are relative terms only and indicative of a general relative orientation only, and do not necessarily indicate perpendicularity, and are also used for convenience to refer to orientations used in the figures, which orientations are used as a matter of convention only and not intended as characteristic of the devices shown. The present invention and the embodiments thereof to be described herein may be used in any desired orientation, and horizontal and vertical walls need generally only be intersecting walls, and need not be perpendicular.
A reactant passage 26, partial detail of which is shown in prior art FIG. 2, is positioned within the volume 24 between the two central horizontal walls 18 and 20. FIG. 2 shows a cross-sectional plan view of the vertical wall structures 28, some of which define the reactant passage 26, at a given cross-sectional level within the volume 24. The reactant passage 26 in FIG. 2 is shaded for easy visibility of the fluid contained therein and forms a two-dimensionally tortuous and winding passage of constant width, in the form of a serpentine, which covers a maximum area of the surface of the plate defining the volume 24. The fluidic connections between the other parts of the microfluidic device 10 and the inlet 30 and outlet 32 of the tortuous reactant passage 26 shown in the cross section of FIG. 1 are provided in a different plane within the volume 12 and/or 14, vertically displaced from plane of the cross-section shown in FIG. 2.
The reactant passage 26 has a constant height in a direction perpendicular to the generally planar walls.
The device shown in FIGS. 1 and 2 serves to provide a volume in which reactions can be completed while in a relatively controlled thermal environment.
In FIG. 3, another prior art device is shown for the specific purpose to mix reactants, especially multiphase systems like immiscible fluids and gas liquid mixtures, and to maintain this dispersion or mixture over a wide range of flow rates. In this device of the prior art, the reactant passage 26 comprise a succession of chambers 34.
Each of such chamber 34 includes a split of the reactant passage into at least two sub-passages 36, and a joining 38 of the split passages 36, and a change of passage direction, in at least one of the sub-passages 36, of at least 90 degrees relative to the immediate upstream passage direction. In the embodiment shown, it may be seen in FIG. 3 that both sub-passages 36 change direction in excess of 90 degrees relative to the immediate upstream passage direction of the reactant passage 26.
Also in the embodiment of FIG. 3, each of the multiple successive chambers 34, for those having an immediately succeeding one of said chambers, further comprises a gradually narrowing exit 40 which forms a corresponding narrowed entrance 42 of the succeeding chamber. The chambers 34 also include a splitting and re-directing wall 44 oriented crossways to the immediately upstream flow direction and positioned immediately downstream of the chamber's entrance 42. The upstream side of the splitting and re-directing wall 44 has a concave surface 46. The narrowing exit 40 from one chamber 34 to the next is desirably on the order of about 1 mm width. The channel desirably may have a height of about 800 μm.
Although good performance has been obtained with devices of this type, in many cases even exceeding the state of the art for a given reaction, it has nonetheless become desirous to improve fluid dynamic performance. In particular, it is desirable to obtain a controlled and well-balanced residence time while simultaneously decreasing the pressure drop caused by the device, while increasing throughput.
In U.S. Pat. No. 7,241,423 (corresponding to US2002106311), “Enhancing fluid flow in a stacked plate microreactor,” parallel channels (see FIG. 37) are used in order to implement an internally parallelized chemical reaction plant for the purpose of provide a microscale reaction apparatus that can provide substantially equal residence time distribution for fluid flow. However this reference does not solve all the issues related to controlled and even distribution of fluid flow.